1. Field of the Invention
This invention relates to a process for preparing organic functional group-containing organopolysiloxanes and also to organopolysiloxanes obtained by the process. The invention also relates to a process for preparing organopolysiloxanes having a polymer moiety having specific types of recurring units. The invention relates to a novel organopolysiloxane oligomer or polymer having both a mercapto functional group and an alkoxy group and a process for preparing such a novel oligomer or polymer.
2. Description of the Related Art
A number of organic functional group-containing organopolysiloxane powder materials have been already proposed including a process wherein tetraalkoxysilanes and organoalkoxysilanes are subjected to co-hydrolysis and polycondensation reaction in the presence of ammonia serving as a catalyst as proposed in Japanese Laid-open Patent Application No. 4-114065 and a process wherein the above co-hydrolysis and polycondensation reaction is conducted in the presence of a hydrofluoric acid (Japanese Laid-open Patent Application No. 62-166887 and Journal of the Japanese Chemical Society 1983 (11), pp. 1577 to 1588).
On the other hand, for the preparation of polysilsesquioxane, there are known a number of processes for hydrolyzing and polycondensing alkoxysilanes such as methyltrimethoxysilane. In most cases, acids, bases or silanol group-containing compounds are used as a catalyst for the hydrolysis and polycondensation. For instance, Japanese Laid-open Patent Application No. 60-118715 proposes a process wherein hydrolysis is effected using an acid catalyst and the resultant reaction system is rendered basic, followed by subsequent polycondensation. In Japanese Laid-open Patent Application 61-854, a partially hydrolyzed polycondensate of a trialkoxysilane is provided as a catalyst for hydrolysis and polycondensation reaction.
As is known in the art, however, the above-stated processes for preparing organic functional group-containing organopolysiloxane powders have problems on (1) uniform dispersion or distribution of the organic functional group in the fine pores of the organopolysiloxane product, (2) a highly reactive organic functional group being kept as it is during and after the course of the hydrolysis and condensation, (3) porosity, and (4) working properties.
With respect to the uniform dispersion or distribution (1), it is not possible to uniformly disperse or distribute the organic functional group throughout the inside of the fine pore according to a dry process wherein a silane coupling agent is sprayed over silicon dioxide powder. For the uniform dispersion and distribution, it has been accepted as being better to make use of a wet process using a co-hydrolysis reaction. With respect to (2) above, where organopolysiloxane powder materials having a highly active organic functional group such as, for example, an epoxy group are prepared by use of an acid or alkali catalyst, the organic functional group is attacked with the acid or alkali catalyst and its functionality is lost. As for the porosity of (3), when using a process which requires a long time before gelation, organopolysiloxane powder particles are gradually deposited one on another, so that porous powder particles are unlikely to obtain. In this connection, it is known that when HF is used, gelation can be completed within a very short time. This eventually leads to the formation of a very porous organopolysiloxane powder substance. However, the use of HF has the problem that the working environment has to be severely controlled owing to the danger involved in HF.
On the other hand, when an alkoxysilane having a highly reactive functional group such as an epoxy group is hydrolyzed and condensed or polycondensed to obtain an epoxy group-containing polysilsesquioxane, the known processes set out hereinbefore have the following drawbacks.
In reaction systems where an acid or base catalyst is used in large amounts, the epoxy group undergoes the electrophilic action owing to H.sup.+ or the nucleophilic attack of the base, and is readily ring-opened or polymerized, thus not permitting the epoxy group to be left stably.
On the other hand, in reaction systems containing an acid or base catalyst having a diluted concentration, the hydrolysis and condensation reaction is unlikely to proceed smoothly. The silanol groups formed by the hydrolysis reaction become stabilized, with the possibility that during a long-term reaction, the acidic silanol group inconveniently serves to open the ring of the epoxy group.
When using an acid or base catalyst, silanol groups which are condensable are left in large amounts after completion of the reaction. This may cause the reaction system to be changed as time passes, resulting, for example, in thickening or gelation of the system.
Most acidic or basic substances are corrosive in nature. Technical consideration should have been taken into account to prevent reactors materials from being corroded. These acids and bases are not beneficial in view of the safety of the working environment.
Thus, in prior art processes, it has been difficult to obtain organic functional group-containing polysilsesquioxane of high quality wherein the functional group is present in the sesquioxane stably without involving any significant change in quality in relation to the time and wherein little problem is involved in operation and safety.
In addition, if it is intended to leave part of an alkoxy group of organic functional group-containing alkoxysilane starting materials after completion of hydrolysis and condensation in reaction systems using an acid or base catalyst, it is essential to carry out partial hydrolysis while controlling an amount of water to be added. The condensation reaction speed in such reaction systems as set out above is not high even when water is employed in large excess. For the partial hydrolysis, a degree of condensation becomes lower. Thus, it will become difficult to prepare a partially hydrolyzed organopolysiloxane product with a desired degree of oligomerization or polymerization.